This invention relates to an intake control system for internal combustion engines and more particularly to an improved induction system for a high performance engine.
As is well known, the valve timing of an internal combustion engine is generally a compromise between achieving maximum power output and smooth running at low engine speeds. Although relatively large valve overlaps (intake and exhaust valves both open at the same time) permit good volumetric efficiency at high engine speeds and maximum power output, idling performance is significantly deteriorated. The reasons engines having high degrees of valve overlap idle poorly is that the exhaust gases tend to flow back into the intake system at low speeds and when both the intake and exhaust valves are open at the same time. As a result, the engines idle poorly. With the so called "sporty type" cars embodying large valve overlaps it has been proposed to employ high idle speeds so as to avoid the rough running which would occur at lower idle speeds. Such high idle speeds, however, result in poor fuel economy and unnecessary noise.
It is, therefore, a principal object of this invention to provide an improved intake control system for an internal combustion engine which permits high power outputs but also offers improved idle operation.
It is another object of this invention to provide an improved system for an engine having a large degree of valve overlap which significantly improves idle operation.
In addition to providing high degrees of valve overlap to improve maximum power output from an engine, it has been proposed to provide multiple valves for each cylinder. The use of two intake ports and valves and two exhaust ports and valves for an engine has also been proposed as a way of increasing maximum power output. When such multiple intake passage engines are employed they exhibit similar running characteristics to engines having high degrees of valve overlap. Even if extreme valve timing is not employed, the use of multiple valves provides a large intake area when the exhaust valves are still open which give rise to the backflow of exhaust gases that deteriorates idle performance.
It is, therefore, a still further object of this invention to provide an improved intake system for an engine having multiple intake passages serving a single chamber.